1. Field of the Presently Disclosed and Claimed Inventive Concepts
The presently disclosed and claimed inventive concept(s) relates generally to a transparent and reusable vacuum infusion heating bag with a heating element for forming polymeric materials. More particularly, the presently disclosed and claimed inventive concept(s) relates to a transparent and reusable vacuum infusion heating bag or a laminate layer with a heating element in resin transfer molding and bagging operation. The presently disclosed and claimed inventive concept(s) further relates to methods of making the vacuum infusion heating bag and using the vacuum infusion heating bag for making composite parts.
2. Background and Applicable Aspects of the Presently Disclosed and Claimed Inventive Concept(s)
Vacuum assisted resin transfer molding (VARTM) is a composite part manufacturing process in which dry fibers of composite material are laid on a forming tool beneath a vacuum bag and vacuum sealed while liquid resin is drawn through the composite material with a vacuum pump. Traditionally, a flow media or resin distribution media made of nylon, plastic, or metal and having a high permeability is placed over the composite material to allow resin to flow over it and subsequently be evenly dispersed throughout the composite material. Additionally, a breather cloth made of fiberglass or peel-ply may be placed beneath the vacuum bag to help pull resin through the material and allow air to be evacuated from between the vacuum bag and the tool. The vacuum bag may then be placed over the composite material, flow media, and breather cloth, and sealed to the forming tool with a vacuum sealing apparatus. A vacuum inlet and a vacuum outlet may allow the liquid resin to be pulled through the composite material. Once the liquid resin is distributed throughout the composite material and the vacuum bag is compressed against the composite material by vacuum force, the vacuum pump may be removed, and the part may then be cured at ambient or by heat to harden the composite part. The vacuum bag is then removed from the forming tool so that the composite part may be separated from the tool.
Because the construction of vacuum bags is time-consuming and expensive, it is desirable that the vacuum bag be reusable. A common vacuum bag material is nylon. For fabricating a composite part on a forming tool having small inside and outside radii, nylon vacuum bags are desirable as the thin nylon film can be laid over the composite part on the forming tool. The nylon film can then be hand conformed to the small inside radii of the forming tool. However, nylon loses considerable resiliency after a single use in an autoclave and therefore cannot be reused to fabricate another composite part. Furthermore, composite parts fabricated using nylon vacuum bags may exhibit flaws in that wrinkles and pinholes may appear due to the bunching up of the nylon film against the forming tool under vacuum pressure. Leakage of the seal between the vacuum bag and the forming tool has also limited production of composite from nylon vacuum bags.
As an alternative, silicone rubber has been utilized to fabricate vacuum bags because it has an elongation of over 500% which allows it to be stretched over small radii on a forming tool. Furthermore, silicone rubber has a maximum exposure temperature of 260° C. which allows for greater curing cycle flexibility. Finally, as compared to nylon, silicone rubber retains its resiliency over many curing cycles and is therefore suitable as a reusable vacuum bag material.
Generally, a transparent or translucent vacuum bag is preferred to allow easy inspection of composite materials to be cured. Much improved visual quality control can be achieved because the resin flow front line can be seen through the transparent or translucent vacuum bag, as well as its penetration through the composite materials.
Some resins have to be cured above room temperature, for example but not by way of limitation, an epoxy resin is cured usually around 60 to 65° C. depending on the process. In order to cure a resin composite part above room temperature, the part has to be heated at a certain temperature. Currently, heat is supplied from a tool side (it is usually called A side on which a part is being laid). The tool side has a built-in heating element. However, the heat is not uniform on the top surface of the part because heat is only provided from the bottom and in some cases a core material in the complex composite part prevents heat to be transferred from the bottom to the top surface (basically the core material acts like insulation). So in those cases, a source of heat from top (it is called B side heating) has to be provided.
Normally, a “heating blower” is used to blow heat in a plastic sealed covered tool. The plastic keeps all the hot air coming out of the blower around the tool area by creating an air bubble or balloon on top of the tool. So this type of heating uses convection to heat the B side. Convection heating is very inefficient compared to conduction heating for heat transfer. Most of heat are lost and cannot be transferred to the B side. As a result, it takes a long time to reach the cure temperature of resin.